The present invention is related to image scanners and in particular to the optical systems of such scanners.
Scanners using array-sensors for scanning pictures are well known in the art. In the last few years array-sensor scanners gained popularity and now play a major role in the scanners market.
One feature of array-sensor scanners is the optical resolution, namely the number of samples per unit of length at the picture plane, used to sample the scanned object.
Some scanners provide a single fixed optical resolution, while others provide variable optical resolution. The latter may be divided into two categories, namely scanners that provide a limited number of discrete optical resolutions and scanners that provide a continuous range of optical resolutions.
U.S. Pat. No. 5,325,217 assigned to Scitex Corporation Ltd., Herzlia, Israel, is an example of a scanner with a continuous range of optical resolutions.
In U.S. Pat. No. 5,325,217, the scanned object""s position along the optical axis is fixed. The single lens and the Charge Couple Device (CCD) sensor can both move along the optical axis, on linear tracks, powered by two separate motors. By setting the positions of the lens and of the CCD, the optical resolution is adjustable in a continuous fashion.
The principle is similar to that of a traditional photographic enlargement machine. The advantage of this method is that one can set any desired optical resolution, within the limitations of the apparatus. However, in this method, a long optical axis is needed to enable a large range of resolutions, which dictates the size of the scanner and the linear tracks are expensive and difficult to handle.
U.S. Pat. No. 5,592,309 assigned to Scitex Corporation Ltd., Herzlia, Israel is an example of a scanner with discrete resolutions.
In U.S. Pat. No. 5,592,309, the distance between the scanned object and the CCD sensor is constant. The scanner has two lenses of different focal lengths, which are exchangeable. Each one of the lenses is positioned at a different point along the optical axis, dependent on its different focal length, to provide a sharp image on the CCD plane. Thus, each lens provides a different optical resolution.
The advantage of this method is that the fixed distance between the scanned object and the CCD provides for a compact design of the scanner.
The disadvantage of this method is that each optical resolution requires a separate lens, which increases the cost of the scanner.
In single optical resolution scanners, apertures and covers can be used to control stray light infiltration while in multi optical resolution scanners, the geometry of the optical system is different at the various resolutions. Thus, a good design for one geometry will usually interfere with the optical system in another geometry.
It is the purpose of the present invention to provide a mechano-optical design for a scanner that overcomes the aforementioned disadvantages of the prior art multi optical resolution scanners.
In one embodiment of the invention, parts of the linear tracks are replaced by relatively low-cost axial bearing, providing a compact optical system design.
In another embodiment of the invention, a dynamic aperture is provided. The aperture is adjustable to provide optimal stray light control for all optical geometries of the optical system.
Thus, in a preferred embodiment, a scanner is provided having inter alia an optical zoom system, which includes a movable lens assembly and a rotatable mirror. The image to be scanned, the optical zoom system and the scanning head are located along an optical axis. The optical resolution of the image, is variable by selectively displacing the lens assembly along the optical axis while simultaneously rotating the rotatable mirror about its center.
In a further preferred embodiment, a scanner is provided having inter alia a variable aperture for controlling the optical resolution and field of view of the image.
There is thus provided in accordance with a preferred embodiment of the present invention, a scanner for scanning an object. The scanner includes a variable sized aperture for controlling stray light, the variable sized aperture being located proximal to the object.
Furthermore, in accordance with a preferred embodiment of the present invention, the scanner further includes an optical zoom system having a movable lens assembly. The variable sized aperture is located between the object and the movable lens assembly.
Furthermore, in accordance with a preferred embodiment of the present invention, the scanner further includes a light source where the variable sized aperture is located between the object and the light source.
Furthermore, in accordance with a preferred embodiment of the present invention, the size of the aperture is adjusted in accordance with the desired field of view.
Additionally, in accordance with a preferred embodiment of the present invention, the scanner also includes an optical system having an optical bench, a lens and a lens displacement mechanism connected to the optical bench.
Furthermore, in accordance with a preferred embodiment of the present invention, the optical system includes a folding mirror and further includes an adjustment mechanism connected to the optical bench. The adjustment mechanism and the lens displacement mechanism are actuated simultaneously.
Furthermore, in accordance with a preferred embodiment of the present invention, the adjusting mechanism includes first and second slider elements, slidingly interleaved one with the other to provide the variable sized aperture. The field of view of the optical system is proportional to the size of the variable sized aperture.
Additionally, in accordance with a preferred embodiment of the present invention, the lens displacement mechanism includes a linear track fixed to the optical bench, a carriage displaceable along the linear track, the lens being mounted on the carriage; and a lens motor attached to the carriage, the lens motor being operative to cause the carriage to travel along the linear track.
Furthermore, in accordance with a preferred embodiment of the present invention, the variable sized aperture is coupled to the lens motor. The adjustment mechanism includes at least one rod about at least one axial bearing point; and a displacement motor coupled to the at least one rod. The folding mirror is pivotally connected to the at least one rod. On activating the displacement motor, the rod pivots about the axial point thereby to control the angular rotation of the folding mirror.
In addition, in accordance with a further preferred embodiment of the present invention, there is thus provided a scanner for scanning an object, said scanner including at least one array sensor, an optical bench, an optical zoom system comprising a folding mirror; and an adjustment mechanism connected to said optical bench for adjusting the position of said folding mirror.